Choosing WLAN equipment

When choosing WLAN equipment, IT buyers need to be careful because of the many different specifications in existence. In particular they must try to avoid problems with backwards compatibility, diminishing product life cycles, upgrade paths and signal congestion.

IT managers in greenfield sites with no legacy WLAN users to support can choose to base their entire wireless infrastructure on just one of the specifications, though they should make sure it is a ratified standard with acceptable vendor support.

The faster 54Mbit/s 802.11a/h or HiperLan/2 technologies offer the highest levels of future-proofing, but 802.11b equipment can provide basic connectivity at a lower price. Buying all the equipment from a signal vendor has advantages from a network management point of view, but any equipment conforming to one of these ratified standards should be interoperable.

The dilemma comes where there are existing users of 802.11b PC Cards and access points on a site. IT managers then need to decide whether to expand that WLAN or add another.

Unfortunately, hardware based on the faster 802.11a/h standards operate in the 5.15 to 5.35GHz waveband, and so cannot communicate with 802.11b devices that transmit in the 2.4GHz waveband. Firms could simply add a separate 802.11a/h wireless subnet. But staff with 802.11b clients would not be able to link to 802.11a/h access points, and those with 802.11a/h hardware would not be able to link to 802.11b access points. This might severely restrict users' ability to roam, although the two WLANs would not suffer from interference because they use different frequencies.

Another alternative is to opt for 802.11g kit, which does transmit signals in the 2.4GHz waveband, and so, theoretically at least, should be backwards compatible with 802.11b equipment. Because 802.11g will offer faster 54Mbit/s transmission rates, there remain some interoperability issues when communicating with 802.11b clients operating at lower speeds, however.

Several manufacturers are integrating both 802.11a/h and 802.11b chips into a single access point, allowing client devices of both types to connect with it and each other. Also, modular access points are starting to appear that can be equipped with either 802.11a or 802.11b access units, or both. These seem to be the safest bet for early adopters - not least, because they can delay the need to make a final decision on which technology to choose until the various WLAN standards have been finally ratified.

Finally, any firm that has already deployed, or is planning to deploy, large numbers of Bluetooth-enabled devices should ideally avoid 802.11b and HiperLan equipment, which transmits in the same 2.4GHz waveband and risks signal interference.

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